A method for signal synchronization detection of a RAKE receiver

Abstract

The RAKE receiver signal synchronization detection method provided in the application comprises the following steps: sorting each correlation value in an initial correlation value set by a RAKE receiver to obtain a final correlation peak position set, selecting a first group of correlation value positions from the final correlation peak position set as a first correlation value position set, and selecting a second group of correlation value positions from the final correlation peak position set as a second correlation value position set; determining the initial position of each correlation value in the second correlation value position set, and selecting the associated position of each correlation value position to be detected based on the initial position to obtain an associated position set of each correlation value position; comparing the associated positions in each associated position set with the final correlation peak positions in the first correlation value position set to determine the number of paths; determining a synchronization detection position based on the number of paths, and processing the received signal based on the synchronization detection position. The synchronization performance under a low signal-to-noise ratio is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of signal processing, and relates to a RAKE receiver signal synchronization detection method. BACKGROUND

[0002] Ionospheric scatter communication has been widely concerned at home and abroad due to its strong confidentiality and long transmission distance, and is considered as one of important communication means in military communication.

[0003] The ionospheric scatter communication system is more susceptible to fading than general communication environment, and the signal-to-noise ratio sharply decreases due to path loss, which will inevitably have a bad impact on timing synchronization of the signal, so accurate synchronization is more necessary.

[0004] The traditional time-frequency synchronization algorithm includes a time domain direct correlation algorithm and a segmented correlation accumulation algorithm based on time domain correlation, wherein the length of the preamble sequence of the time domain direct correlation algorithm is very long to achieve ideal synchronization performance, and the longer the synchronization header is, the greater the calculation amount is, which will increase the difficulty of engineering implementation, and the increase of the calculation amount will lead to the increase of FPGA resources, and the segmented correlation accumulation algorithm based on time domain correlation has multiple correlation peaks in the synchronization process, which is not conducive to the setting of the detection threshold, and slight deviation will cause missed detection or false alarm.

[0005] The prior art proposes a segmented correlation accumulation algorithm based on Barker code weighting, that is, the Barker code is used for weighting processing when the preamble sequence is constructed at the sending end, a bit Barker code is used for a segment of the preamble sequence, and the receiver performs correlation between each segment of the preamble sequence and the local ZC sequence when performing timing synchronization, and the same Barker code weighting at the sending end is used for de-weighting processing, when the sequence completely enters the correlation window, the correlation peak at the synchronization point position remains unchanged, and the corresponding accumulation value at other positions which do not completely enter the correlation window is equal to positive A or 0, that is, the Barker code weighting destroys the repeated structure of the original sequence, avoids the multiple peak situation of the corresponding accumulation value, and shortens the time. Then the RAKE combining processing is performed on the correlation peak after correlation. The RAKE receiving technology is one of effective anti-fading methods, it is a final receiver which changes vector combination into algebraic summation by taking out the multi-path component with an amplitude obviously greater than the noise background, correcting the delay and phase of the multi-path component, aligning the multi-path component at a certain time, and combining according to certain rules, which can strengthen the signal at a certain position, so that the noise part and the synchronization peak are more different, which will be conducive to the setting of the synchronization threshold, so as to improve the synchronization performance. However, the RAKE combining only selects the multi-path signal to be combined, and the determination of the synchronization position is still mainly based on the position of the maximum value, so compared with the original RAKE combining, the synchronization performance under low signal-to-noise ratio is not greatly improved. SUMMARY

[0006] The application provides a RAKE receiver signal synchronization detection method, which can improve the synchronization performance under a low signal-to-noise ratio.

[0007] In a first aspect, the application provides a RAKE receiver signal synchronization detection method, which comprises the following steps: a receiving end receives a synchronization sequence weighted by a sidelobe-free Barker code sequence on a ZC sequence sent by a sending end, and obtains an initial correlation value set based on the received synchronization sequence and a ZC conjugate sequence, each correlation value having an initial position in the initial correlation value set; the RAKE receiver sorts each correlation value in the initial correlation value set to obtain a final correlation peak position set, each correlation value having a final correlation peak position in the final correlation peak position set; a first group of correlation value positions is selected from the final correlation peak position set as a first correlation value position set, and a second group of correlation value positions is selected from the final correlation peak position set as a second correlation value position set; the initial position of each correlation value in the second correlation value position set is determined, and the associated positions of each correlation value position are selected based on the initial positions to obtain an associated position set of each correlation value position; the associated positions in each associated position set are compared with the final correlation peak positions in the first correlation value position set to determine the number of paths; a synchronization detection position is determined based on the number of paths, and the received signal is processed based on the synchronization detection position.

[0008] Before the step of receiving, by the receiving end, the synchronization sequence weighted by the sidelobe-free Barker code sequence on the ZC sequence sent by the sending end and obtaining the initial correlation value set based on the received synchronization sequence and the ZC conjugate sequence, the method comprises the following steps: the sending end extends the head and tail of an initial Barker code sequence to obtain a double-sequence Barker code; a Barker code sequence matrix is obtained based on a synchronization header and the double-sequence Barker code; a part of the Barker code sequence matrix is converted from parallel to serial, and is crossed according to the principle that odd bits remain unchanged and even bits are changed to their opposite numbers to form a sidelobe-free Barker code sequence; the sidelobe-free Barker code sequence is multiplied by the ZC sequence of the synchronization header to obtain a to-be-sent sequence, and the to-be-sent sequence is sent.

[0009] The step of receiving, by the receiving end, the synchronization sequence weighted by the sidelobe-free Barker code sequence on the ZC sequence sent by the sending end and obtaining the initial correlation value set based on the received synchronization sequence and the ZC conjugate sequence comprises the following steps: the receiving end performs serial-parallel conversion on the to-be-sent sequence to obtain a first matrix; the first matrix is multiplied by the sidelobe-free Barker code and is subjected to de-weighting processing to obtain a de-weighted matrix; the de-weighted matrix is accumulated by column to obtain corresponding accumulated values, and the corresponding accumulated values are conjugate-correlated with the ZC sequence to obtain the initial correlation values.

[0010] The RAKE receiver sorts each correlation value in the initial correlation value set to obtain a final correlation peak position set, each correlation value having a final correlation peak position in the final correlation peak position set, the step of selecting a first group of correlation value positions from the final correlation peak position set as a first correlation value position set comprises: selecting a first preset number of correlation value positions with larger modulus values as the first correlation value position set.

[0011] The step of selecting a second group of correlation value positions from the final correlation peak position set as a second correlation value position set comprises: determining a second preset number of the second group of correlation value positions based on a minimum time delay and a system bandwidth; and selecting a second preset number of correlation value positions with larger modulus values from the final correlation peak position set as the first correlation value position set.

[0012] The step of selecting a first group of correlation value positions from the final correlation peak position set comprises: selecting a first preset number of correlation value positions with larger modulus values as the first correlation value position set.

[0013] The step of selecting a first group of correlation value positions from the final correlation peak position set comprises: selecting a first preset number of correlation value positions with larger modulus values as the first correlation value position set.

[0014] The step of determining the synchronization detection position based on the path number comprises: in response to the path number having a maximum value, taking the maximum value in the path number as the synchronization detection position; in response to the path number not having a maximum value, comparing the peak values corresponding to the maximum path number, taking the maximum peak value, and taking the position corresponding to the maximum peak value as the synchronization detection position.

[0015] The step of processing the received signal based on the synchronization detection position comprises: accumulating the correlation peak values in the final correlation value set item by item to obtain an accumulation result; determining whether the correlation peak value in the accumulation result increases the maximum correlation value; if yes, determining that the correlation peak value is a multipath signal, performing phase compensation on the multipath signal, and aligning and superimposing the compensated multipath signal; moving the superimposed maximum value to the synchronization detection position to complete the RAKE combination.

[0016] The RAKE receiver signal synchronization detection method provided in the application comprises: a receiving end receiving a synchronization sequence obtained by weighting a ZC sequence by a sidelobe-free Barker code sequence sent by a sending end, and obtaining an initial correlation value set based on the received synchronization sequence and a ZC conjugate sequence, each correlation value having an initial position in the initial correlation value set; the RAKE receiver sorts each correlation value in the initial correlation value set to obtain a final correlation peak position set, each correlation value having a final correlation peak position in the final correlation peak position set; selecting a first group of correlation value positions from the final correlation peak position set as a first correlation value position set, and selecting a second group of correlation value positions from the final correlation peak position set as a second correlation value position set; determining the initial position of each correlation value in the second correlation value position set, and selecting an associated position of each correlation value position based on the initial position to obtain an associated position set of each correlation value position; comparing the associated positions in each associated position set with the final correlation peak positions in the first correlation value position set to determine a path number; determining a synchronization detection position based on the path number, and processing the received signal based on the synchronization detection position. The synchronization performance under a low signal-to-noise ratio can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a flowchart of an embodiment of the RAKE receiver signal synchronization detection method of the application;

[0018] Figure 2 is a schematic diagram of detection probability when the multipath combination range number is different under a scattering channel in S94;

[0019] Figure 3 is a specific flowchart of the application. DETAILED DESCRIPTION

[0020] In order to further clarify the technical means and effects taken by the present application to achieve the predetermined inventive objectives, the present application is described in detail below in conjunction with the accompanying drawings and specific embodiments. The foregoing and other technical contents, features and effects of the present application can be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. The accompanying drawings are provided for reference and explanation only and do not limit the technical solutions of the present application.

[0021] Please refer to Figure 1 , Figure 1 The flowchart of an embodiment of the RAKE receiver signal synchronization detection method of the present application is shown in detail, which specifically includes:

[0022] Step S11: The receiving end receives the synchronization sequence weighted by the sidelobe-free Barker code sequence to the ZC sequence sent by the sending end, and obtains an initial correlation value set based on the received synchronization sequence and the ZC conjugate sequence. Each correlation value has an initial position in the initial correlation value set.

[0023] Specifically, the specific process of the present application is described below. Figure 3

[0024] The sending end extends the beginning and end of the initial Barker code sequence to obtain a double-sequence Barker code. For example, the sending end adds 1 at the front and 13-bit inverse Barker code at the back of the 13-bit Barker code sequence "[1 1 1 1 1 -1 -1 1 1 -1 1 -1 1]" to form the double-sequence Barker code shown below, which is in the form of "[1 1 1 1 1 1 -1 -1 1 1 -1 1 -1 1 -1 -1 -1 -1 -1 1 1 -1 -1 1 -1 1 -1]".

[0025] Based on the synchronization header and the double-sequence Barker code, a Barker code sequence matrix is obtained. Specifically, the length of the synchronization header is divided by the length of the double-sequence Barker code to obtain a sequence length b, so that the synchronization header with a length of b*a is vertically expanded into a Barker code sequence matrix with a length of b*a according to the double-sequence Barker code.

[0026] The part of the Barker code sequence matrix is converted into parallel-serial conversion, and the cross is performed according to the principle that the odd bits remain unchanged and the even bits become opposite numbers to form a sidelobe-free Barker code sequence. Specifically, the Barker code sequence length a is odd here; the first half of the Barker code matrix is unchanged, and the second half of the Barker code matrix ​The even-numbered bits are crossed over according to the principle that the odd-numbered bits are not changed and the even-numbered bits are changed into opposite numbers after the parallel-serial conversion of the Barker code matrix, the front half and the rear half are combined together to form a new Barker code sequence, and the Barker code sequence formed in this form is called a sidelobe-free Barker code in the application because the sidelobe is eliminated.

[0027] The sidelobe-free Barker code sequence is multiplied by the ZC sequence of the synchronization header to obtain a to-be-sent sequence, and the to-be-sent sequence is sent. The sequence obtained by multiplying the Barker code sequence by the ZC sequence of the synchronization header is added to the sending sequence for sending. Specifically, the to-be-sent sequence is added to the to-be-sent signal for sending together.

[0028] In an embodiment, the receiving end performs serial-parallel conversion on the to-be-sent sequence to obtain a first matrix. Specifically, the receiving end performs serial-parallel conversion on the received sequence to obtain a first matrix of b*a in length. The first matrix is multiplied by the sidelobe-free Barker code and subjected to de-weighting processing to obtain a de-weighted matrix; the de-weighted matrix is accumulated by column to obtain a corresponding accumulated value, and the corresponding accumulated value is conjugate-correlated with the ZC sequence to obtain the initial correlation value. The matrix is multiplied by the sidelobe-free Barker code generated by the sending end and subjected to de-weighting processing; the a column correlation values are accumulated after de-weighting processing; and the corresponding accumulated value is conjugate-correlated with the local ZC sequence in the signal acquisition process of the matching filter to obtain the initial correlation value.

[0029] Step S12: The RAKE receiver sorts each correlation value in the initial correlation value set to obtain a final correlation peak position set, and each correlation value has a final correlation peak position in the final correlation peak position set.

[0030] Specifically, the RAKE receiver sorts each correlation value in the initial correlation value set in descending order of modulus to obtain a final correlation value set; each correlation value in the final correlation value set corresponds to a final correlation peak position, and the final correlation peak positions of all correlation values form the final correlation peak position set. The positions after arrangement are denoted as L1, L2, L3,..., Ln respectively. n .

[0031] The maximum peak value and the maximum noise value are found out from the final correlation peak position set; if the maximum peak value is greater than n times of the maximum noise value, the maximum peak value is the synchronization detection position; n>2; otherwise, step S13 is performed: a first group of correlation value positions in the final correlation peak position set are selected. It can be understood that if the maximum peak value is greater than n times of the maximum noise value, it is a high signal-to-noise ratio, and the synchronization detection position can be directly confirmed at this time.

[0032] Step S13: selecting a first group of correlation value positions from the final correlation peak position set as a first correlation value position set, and selecting a second group of correlation value positions from the final correlation peak position set as a second correlation value position set.

[0033] Specifically, a first preset number of correlation value positions with larger modulus values are selected from the final correlation peak position set as the first correlation value position set. The largest 64 synchronization peak values after the sorted correlation peak values are taken as the first correlation value set. That is, the positions corresponding to the 64 synchronization peak values taken in the order from small to large are position64=L 65 ,... L n .

[0034] In an embodiment, a second preset number of the second group of correlation value positions is determined based on the minimum time delay and the system bandwidth; and a second preset number of correlation value positions with larger modulus values are selected from the final correlation peak position set as the first correlation value position set.

[0035] In a specific embodiment, the specific method of determining the second preset number is as follows:

[0036] S71: determining the minimum time delay τ min and the system bandwidth B;

[0037] S72: calculating the number L=τ min *B when the time delay is τ min .

[0038] S73: determining 5 points on both sides of L with L as the center, i.e., L b =L-5,..., L+5.

[0039] S74: taking the first value in L b , and calculating the detection probability under different SNRs;

[0040] S75: repeating step S74 to calculate the detection probability under different SNRs when L b takes different values.

[0041] S76: finding the number L i corresponding to the highest detection probability, which is the second preset number.

[0042] In an embodiment, the second preset number is also referred to as the judgment multipath number. Assuming that the second preset number is 15, the largest 15 synchronization peak values after the sorted final correlation value set are taken, i.e., the positions corresponding to the 15 synchronization peak values taken in the order from small to large are position15=L 16 ,..., L.n .

[0043] Step S14: determining an initial position of each correlation value in the second correlation value position set, and selecting an associated position of each correlation value position to be tested based on the initial position, to obtain an associated position set of each correlation value position.

[0044] Specifically, the associated position needs to be further determined, and then the associated position set is obtained. In a specific embodiment, a first point number corresponding to a maximum time delay and a second point number corresponding to a minimum time delay are determined; a point combination is obtained by taking a preset step value from the vicinity of the first point number to m times of the second point number; a detection probability change of each point number in the point combination under a plurality of fixed signal-to-noise ratios is determined; a point number corresponding to the highest detection probability is taken as a merging number; an associated position of each correlation value is determined based on the merging number; an associated position of each correlation value position to be tested is selected based on the initial position, to obtain an associated position set of each correlation value. Specifically, it includes:

[0045] S91: respectively determining a first point number M max and a second point number M min corresponding to a maximum time delay τ max and a minimum time delay τ min .

[0046] S92: taking numbers around M min and in the middle of 2M max as values with a step of 2 n ; and respectively denoted as M

[0047] S93: giving four fixed low signal-to-noise ratios SNR1, SNR2, SNR3 and SNR4.

[0048] S94: measuring a change of a Rake merging number M with a detection probability when a signal-to-noise ratio is fixed as SNR1; for details, please refer to Figure 2 .

[0049] S95: repeating step S94 to obtain changes of the Rake merging number M with the detection probability under four low signal-to-noise ratios.

[0050] S96: finding a merging number corresponding to the highest detection probability, that is, obtaining an associated position set of each correlation value.

[0051] Step S15: comparing an associated position in each of the associated position sets with a final correlation peak position in the first correlation value position set, to determine a path number.

[0052] In an embodiment, assuming the set of associated positions is 64, the maximum peak value of the 15 synchronization peaks is taken, the position corresponding to the maximum peak value is Ln, and the 64 positions on the left and right of the maximum correlation peak in the original correlation sequence are taken, i.e., L n-64 to L n+64 The positions of the 129 paths are compared with the positions in position 64 in S6, and the number of positions that are equal is stored as the path number N1.

[0053] The second largest peak value of the 15 synchronization peaks is taken, the position corresponding to the second largest peak value is L n-1 The 129 positions in the range of 64 paths on the left and right of the second largest correlation peak in the original correlation sequence are taken, the positions of the 129 paths are compared with the positions in position 64 in S6, and the number of positions that are equal is stored as the path number N2, and so on until the path numbers corresponding to all positions in the synchronization peak position 15 are compared, and they are all stored as the path number N=N1, N2,..., N 15 .

[0054] Step S16: determining the synchronization detection position based on the path number, and processing the received signal based on the synchronization detection position.

[0055] In an embodiment, in response to the presence of a maximum value in the path number, the maximum value in the path number is taken as the synchronization detection position; in response to the absence of a maximum value in the path number, the peak values corresponding to the maximum path numbers are compared, the maximum peak value is taken, and the position corresponding to the maximum peak value is taken as the accurate synchronization position.

[0056] Specifically, the maximum value N max of the 15 stored numbers is compared, if there is, the correlation peak position corresponding to the maximum value is taken as the correct position of the synchronization peak, if there is not, the peak values corresponding to several maximum path numbers are compared, the maximum peak value is taken, and the position corresponding to the maximum peak value is taken as the accurate synchronization position.

[0057] In an embodiment, the correlation peak values in the final set of correlation values are added one by one to obtain an accumulated result; it is determined whether the correlation peak value in the accumulated result will increase the maximum correlation value; if yes, it is determined that the correlation peak value is a multipath signal, the multipath signal is phase compensated, and the compensated multipath signals are aligned and superimposed; the maximum value after superposition is moved to the synchronization detection position to complete RAKE combination

[0058] In an embodiment, after the position of the synchronization is determined, it is judged whether the superposition of the rest of the correlation values in the initial correlation value set except the maximum correlation value will increase the peak value or not, if not, it is determined as a single-path signal, and the signal is directly output. If yes, it is determined as a multi-path signal, the maximum N multi-path signals meeting the condition are taken out for phase compensation, and then the compensated multi-path signals are aligned and superposed, the maximum value after superposition is taken as the synchronization peak value Peak, and the position corresponding to the synchronization peak value is taken as the synchronization position.

[0059] Selection of multi-path signals in multi-path combination (superposition). Since the purpose of multi-path combination is to enhance the signal strength at the synchronization position, the multi-paths that can be combined are selected in the present application.

[0060] Suppose the maximum multi-path peak value corresponds to x, and the other multi-path signals can be represented as a1x, a2x, … a n x, at this time, the condition that the peak value after combination can make the synchronization peak value larger after normalization should be met, that is,

[0061]

[0062] which can be simplified as:

[0063]

[0064] Let t = 1 + a1 + a2 + a3 + … + a n-1 , and the substitution gives:

[0065]

[0066] Simplifying gives:

[0067] t 2 -2Na t-Na 2 <0

[0068] n n

[0069] The correlation peak value meeting this condition is taken as the multi-path signal that can be combined.

[0070] In an embodiment, if the synchronization position is in the noise area and exceeds the threshold value obtained under the constant false alarm, it is considered as a false alarm; if the synchronization position is in the signal area and does not exceed the threshold value obtained under the constant false alarm, it is considered as a missed detection; if the synchronization position is in the signal area and exceeds the threshold value obtained under the constant false alarm, it is considered as a successful synchronization detection.

[0071] In the first aspect of the present application, an improvement is made to a Barker code sequence. The present invention transforms the Barker code weighting in the existing 13-bit Barker code weighted segmented correlation joint RAKE reception algorithm into an a-bit sidelobe-free Barker code sequence weighting. The a-bit sidelobe-free Barker code sequence is an improved form consisting of a 1+13-bit Barker code and a 13-bit inverse Barker code. Specifically, the synchronization header length (b*a) is divided by the sidelobe-free Barker code length (a) to obtain the sequence length b. The a-bit Barker code is vertically extended by b data lengths to generate a b*a Barker code matrix sequence. The first half of the b*a-bit Barker code matrix sequence is then converted to the first half. The matrix of the second half remains unchanged. After parallel-to-serial conversion, the Barker code matrix is ​​interleaved according to the principle that odd bits remain unchanged and even bits are reversed. The first and second halves are combined to form the sidelobe-free Barker code of the present invention. Compared to existing Barker code weighted synchronization techniques, the sidelobe-free Barker code not only offers better detection performance in low signal-to-noise ratio (SNR) conditions in scattering channels, but also requires a correlation sequence length that is almost half that of a 13-bit Barker code, simplifying the implementation of the correlation.

[0072] A second aspect of the application relates to the determination of synchronization threshold. If fixed threshold is used, when interference intensity changes, false alarm probability also changes thereupon. And there is multipath interference in ionospheric scattering communication. For the sudden change of signal and different channel qualities in the communication environment, it is necessary to adopt adaptive threshold technology so that signal can reduce false alarm probability as much as possible and improve detection probability when noise intensity constantly changes. Therefore, the present invention can measure the false alarm probability under different signal-to-noise ratio conditions and be the threshold value of 0.001, using this value as the adaptive detection threshold.

[0073] The third aspect of this application is to judge whether it is a high signal-to-noise ratio situation and make corresponding processing. The position of the maximum peak under high signal-to-noise ratio is the correct synchronization position. If the acquisition of the synchronization position under high signal-to-noise ratio is processed in multiple steps like under low signal-to-noise ratio to determine the accurate synchronization position, although it can be determined correctly, it also takes a certain amount of time to implement. In order to save synchronization time, the situation where the signal-to-noise ratio is high can be handled separately. Corresponding conditions are set in this patent, and all areas outside the 64 paths on both sides of the maximum peak are regarded as noise areas. The maximum value in the noise area is taken out and recorded as the maximum noise. The maximum noise and the maximum peak are compared. If the maximum peak is greater than twice the maximum noise, it is considered that the signal-to-noise ratio is high at this time. The position corresponding to the maximum peak after correlation can be directly used as the synchronization position. Otherwise, the judgment is made according to the steps for judging the synchronization position under low signal-to-noise ratio.

[0074] The fourth aspect of the application relates to the determination of the synchronization position. Firstly, the received signal is correlated with the local sequence, the correlation peaks after correlation are sorted in ascending order, the positions corresponding to the largest 64 correlation peaks and the largest 15 correlation peaks are taken from the back, then the positions corresponding to the correlation peaks of 129 paths on the left and right of the largest correlation peak in the original sequence are taken, the positions of the correlation peaks of the 129 paths and the largest 64 correlation peaks taken out are compared, and the number of positions that are the same is recorded in the path number; the 129 paths at the original position of the second largest peak and the largest 64 correlation peaks taken out are compared, and the number of positions that are the same is recorded in the same way; the path number corresponding to the largest 15 paths is obtained, if the largest path number is only one, the position corresponding to the peak with the largest path number is taken out and recorded as the accurate synchronization position, if the largest path number has multiple, the correlation peaks corresponding to the multipath signals at these positions are compared, and the position with the largest correlation peak is taken out as the synchronization position.

[0075] The fifth aspect of the application relates to the determination of the range of the number of multipaths on the left and right of the largest peak and the determination of the judgment multipath number for path number comparison. The range of the number of multipaths on the left and right of the largest peak is related to the maximum multipath delay and the minimum multipath delay, the maximum multipath delay and the minimum multipath delay correspond to different numbers of multipaths respectively, the number of multipaths in this interval is taken with a step of 2 n as the basis, the corresponding range of the number of multipaths is 64 paths; the judgment multipath number for path number comparison is related to the minimum delay, this value fluctuates near the minimum delay, the number of multipaths is obtained by using the delay and the system bandwidth, and the number of multipaths obtained by using the minimum delay is mainly used, the number of multipaths on both sides of the number of multipaths is taken with a step of 5, and the number of multipaths with high detection probability under different signal-to-noise ratios is used as the judgment multipath number.

[0076] The sixth aspect of the application relates to the determination of the range of the number of multipaths on the left and right of the largest peak and the determination of the judgment multipath number for path number comparison. The range of the number of multipaths on the left and right of the largest peak is related to the maximum multipath delay and the minimum multipath delay, the maximum multipath delay and the minimum multipath delay correspond to different numbers of multipaths respectively, the number of multipaths in this interval is taken with a step of 2

[0077] The application provides a synchronization method of a scattering channel under a low signal-to-noise ratio condition based on an improved Barker code weighted ZC sequence joint RAKE receiving.

[0078] The application changes the 13 Barker code weighted ZC sequence in the existing segmented correlation joint RAKE receiving algorithm based on Barker code weighting to a bit a sidelobe-free Barker code weighted ZC sequence, and provides an improvement process of the a bit sidelobe-free Barker code, that is, the length of a synchronization header of b*a is divided by the length of a double sequence Barker code a to obtain a sequence length b, the synchronization header of the length of b*a is longitudinally expanded to a Barker code sequence matrix of b*a according to the double Barker code sequence, and the Barker code sequence length a is an odd number. The last half part of the Barker code matrix is converted from parallel to serial, and then is crossed according to the principle that the odd bits remain unchanged and the even bits are changed to the opposite numbers. The first half part and the last half part are combined together to form the sidelobe-free Barker code sequence. After the ZC sequence of the synchronization header is weighted and transmitted by using the sidelobe-free Barker code sequence, the synchronization performance of the receiving end is slightly enhanced, but the correlation sequence length used by the receiving end is almost reduced by half compared with the correlation length of the 13 bit Barker code weighting, so that the implementation of the entire correlation is more simple, and the time and resources required in the implementation of the correlation are reduced.

[0079] The RAKE combining is improved from multiple aspects, including setting the threshold under the scattering channel to an adaptive threshold under the constant false alarm, processing the signal under the high signal-to-noise ratio and the low signal-to-noise ratio, judging and processing whether there is a single path, and improving the accurate determination of the synchronization position under the scattering channel and the selection of the multipath signal when the multipath combining, so that the synchronization performance under the ionospheric scattering channel and the low signal-to-noise ratio is improved.

[0080] The above is only the implementation method of the application, and does not limit the patent range of the application, and any equivalent structure or equivalent flow transformation using the content of the specification and the drawings, or direct or indirect application in other related technical fields, is also included in the patent protection range of the application.

Claims

1. A method of signal synchronization detection for a RAKE receiver, characterized by, The method comprises the following steps: The receiving end receives the synchronization sequence weighted by the ZC sequence and the sidelobe-free Barker code sequence sent by the sending end, and obtains an initial correlation value set based on the received synchronization sequence and the ZC conjugate sequence, each correlation value having an initial position in the initial correlation value set; specifically, the receiving end performs serial-parallel conversion on the to-be-sent sequence to obtain a first matrix; multiplies the first matrix by the sidelobe-free Barker code and performs de-weighting processing to obtain a de-weighted matrix; accumulates the de-weighted matrix by column to obtain a corresponding accumulated value, and performs conjugate correlation between the corresponding accumulated value and the ZC sequence to obtain the initial correlation value; The RAKE receiver sorts each correlation value in the initial correlation value set to obtain a final correlation peak position set, each correlation value having a final correlation peak position in the final correlation peak position set; specifically, the RAKE receiver sorts each correlation value in the initial correlation value set in a descending order of modulus to obtain a final correlation value set; each correlation value in the final correlation value set corresponds to a final correlation peak position, and the final correlation peak positions of all correlation values form the final correlation peak position set; A first group of correlation value positions is selected from the final correlation peak position set as a first correlation value position set, and a second group of correlation value positions is selected from the final correlation peak position set as a second correlation value position set; specifically, a first preset number of correlation value positions with larger modulus are selected from the final correlation peak position set as the first correlation value position set; a second preset number of the second group of correlation value positions is determined based on the minimum time delay and the system bandwidth; the second preset number of correlation value positions with larger modulus corresponding to the modulus are selected from the final correlation peak position set as the second correlation value position set; The initial position of each correlation value in the second correlation value position set is determined, and the associated position of each to-be-tested correlation value position is selected based on the initial position to obtain an associated position set of each correlation value position; specifically, the initial position of each correlation value in the second correlation value position set is determined; the first point number corresponding to the maximum time delay and the second point number corresponding to the minimum time delay are determined; the point combination is obtained by taking a preset step value from the vicinity of the first point number to m times the second point number; the detection probability change of each point number in the point combination under a plurality of fixed signal-to-noise ratios is determined; the point number corresponding to the highest detection probability is taken as the merging number; the associated position of each correlation value is determined based on the merging number; the associated position of each to-be-tested correlation value position is selected based on the initial position to obtain an associated position set of each correlation value. The associated positions in each of the associated position sets are compared with the final correlation peak position in the first correlation value position set to determine a path number; specifically, a plurality of synchronization peaks are taken from the associated position set, and from all the taken synchronization peaks, a current peak is taken in order from large to small, and for the current peak, a same number of left and right paths of the current peak in the original correlation sequence are taken according to the position of the current peak, and the positions of the paths are compared with the final correlation peak position in the first correlation value position set, and the number of equal positions is saved as the path number; a synchronization detection position is determined based on the path number, and the received signal is processed based on the synchronization detection position; specifically, in response to the path number having a maximum value, the maximum value in the path number is taken as the synchronization detection position; in response to the path number not having a maximum value, the peaks corresponding to the maximum path number are compared, and the maximum peak is taken, and the position corresponding to the maximum peak is taken as the synchronization detection position; the correlation peaks in the final correlation value set are accumulated item by item to obtain an accumulation result; it is determined whether the correlation peak in the accumulation result will increase the maximum correlation value; if yes, the correlation peak is determined to be a multipath signal, the multipath signal is phase compensated, and the compensated multipath signal is aligned and superimposed; the maximum value after superposition is moved to the synchronization detection position to complete RAKE combining.

2. The method of claim 1, wherein, Before the step of receiving the synchronization sequence weighted by the ZC sequence of the null sidelobe Barker code sequence sent by the sending end by the receiving end, and obtaining an initial correlation value set based on the received synchronization sequence and the ZC conjugate sequence, comprising: The sending end extends the head and tail of the initial Barker code sequence to obtain a double-sequence Barker code; Based on the synchronization header and the double-sequence Barker code, a Barker code sequence matrix is obtained; The part of the Barker code sequence matrix is converted into parallel-serial conversion, and is crossed according to the principle that the odd bits remain unchanged and the even bits become opposite numbers to form a null sidelobe Barker code sequence; After multiplying the null sidelobe Barker code sequence and the ZC sequence of the synchronization header, a to-be-sent sequence is obtained, and the to-be-sent sequence is sent.

3. The method of claim 1, wherein the step of detecting the synchronization comprises: After the step of the RAKE receiver sorting each correlation value in the initial correlation value set to obtain a final correlation peak position set, comprising: Finding the maximum peak and the maximum noise value from the final correlation peak position set; If the maximum peak is greater than n times of the maximum noise value, the maximum peak is the synchronization detection position; n≥2; Otherwise, the step of selecting a first group of correlation value positions from the final correlation peak position set is performed.

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